Liquid crystal display is the most popular flat panel display at present. Thin Film Transistor Liquid Crystal Display (TFT-LCD) is a staple liquid crystal display. Display device is an important component in the liquid crystal display. In general, a display device comprises an array substrate and a color filter (CF) substrate aligned with each other to form a cell, a liquid crystal layer being filled between the array substrate and the color filter substrate. In order that the display device has a certain cell gap, photo spacers should be disposed between the array substrate and the color filter substrate. The color filter substrate may comprise a base substrate, and a black matrix and a color matrix pattern formed above the base substrate. A cover layer is formed above the black matrix and the color matrix pattern, and the photo spacers may be formed on the cover layer. The photo spacers may be formed by depositing material layer of photo spacer and then patterning the material layer of photo spacer. The patterning process may include exposing, developing and etching. Generally, photo spacers may be classified into main photo spacers (main PSs) and sub photo spacers (sub PSs). Main PSs and sub PSs are located on the cover layer with a flat surface, and the height of main PS is larger than that of sub PS. Thus, there is main-sub segment difference (M-S segment difference) between the main PS and the sub PS, which is a height difference between top of the main PS and top of the sub PS. After the color filter substrate and the array substrate are aligned with each other to form a cell, the main PSs are supporting directly between the color filter substrate and the array substrate as main support, while the sub PSs do not contact with the array substrate under normal circumstances. Only when an external force acts on the substrates will the sub PSs play an auxiliary support role so as to prevent the main PSs from being damaged due to overpressure.
The main PSs and the sub PSs are fabricated simultaneously by a patterning process at a time. Fabricating main PSs and sub PSs with a M-S segment difference less than 0.2 μm therebetween can be implemented merely by adjusting process parameters in the patterning process. Fabricating main PSs and sub PSs with a M-S segment difference less than 0.6 μm and more than 0.2 μm therebetween can be implemented by using a half-tone mask in the patterning process. Transmittance of a portion of the half-tone mask corresponding to the main PSs is different from that of a portion of the half-tone mask corresponding to the sub PSs. Accordingly, exposure intensities of different portions are different in the exposing process, ultimately resulting in the main PSs and the sub PSs with respective heights. However, in practice, it is difficult to form main PSs and sub PSs with larger M-S segment difference by using the half-tone mask.
In sum, with the technical solution of the prior art, M-S segment difference between the formed main PSs and sub PSs is small, and it is difficult to form main PSs and sub PSs with larger M-S segment difference.